1988 Mercury 90 RPM Issue

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Razor70

Recruit
Joined
Apr 11, 2021
Messages
3
Intermittent rpm issue, can run fine all day then won't go over 3000 rpm's.
Last time out ran fine until heading in, had throttle at full but only hit 3000 rpm's,
left throttle at full then after about 2 minutes rpm's just shot up and ran fine. Squeezing the ball doesn't change anything.
I changed the Trigger only because the wires were mush. New spark plugs, fuel filter, ran a gallon of Seafoam mix through engine, all voltages test great at idle on the muffs using DVA adaptor for
peak voltage readings. I do have 15 volts charging battery.
Any thoughts?
 
Texasmark

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,869
How long were you taking to "head in" (really how long had the engine been running constantly) and how long did RPM reduction last. If it quit what did you do to make it quit?
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,509
Mercury motors often have high and low speed stator windings. If the high speed stator windings went bad, RPM will be limited. You might ohm them out.
 
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Razor70

Recruit
Joined
Apr 11, 2021
Messages
3
The rpm issue can happen immediately after launch or when it's been running for two hours. when it will only go up to 3000 rpm's it happens whether you go full throttle fast and gradual to full throttle. I didn't do anything when it shot back up to full rpm's, I left the throttle lever at full speed, previously I pumped the primer bulb with no change. It is intermittent.
I previously DVA voltage tested the stator but I'll ohm's test it and see what the readings are. About five years ago I changed the Stator because I lost low speed stator windings. I forgot the company I bought it from but it was a more reputable brand.
 
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